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You can combine accounts by merging them together. This is a process which can't be undone afterwards. You'll also want to be aware that QuickBooks uses some default accounts for certain features, and these types of accounts won't be able to be merged. Additionally, accounts connected to online banking won't be able to be merged either.
Before merging accounts, you'll need to confirm you're in Accountant view. This can be checked by using your Gear icon, then clicking Switch to Accountant view. If it says "Switch to Business view", this means you're already in Accountant view.
Here's how to merge accounts once you're prepared:
If you're merging accounts that have reconciliation reports, save the reports first. Your account being merged may not keep its reconciliation history. The transactions remain on your merged account and stay reconciled. You'll also want to be aware that if both account registers have an opening balance equity transaction, which ever one has the most recent date will need to be deleted prior to merging. Your older transaction becomes the opening balance of your newly merged account.
Use the Gear icon, then go to Chart of accounts.
Find which account you want to keep and click its Drop-Down Arrow (▼) in your Action column, then choose Edit.
Note the Save account under (Account Type), Account name (name), and Tax form section (Detail Type) of your account. These must be the same between your accounts you're merging.
Check if the account is a sub/parent account. Your names for subaccounts are indented in the Name column of your Chart of accounts list. If it is, take note of which parent account it's tied to.
From the Chart of accounts screen, find your account you don't want to keep, then use its Drop-Down Arrow (▼) icon and click Edit.
Change the Account name (Name) and Tax form section (Detail Type) so your other account's info matches the account you want to keep.